containsAll return False when comparing two ArrayList of object

Question

I have two ArrayList as :

ArrayOne

ClassPojo [Name ="XXX", FilterID = 4]
ClassPojo [Name = "ZZZ", FilterID = 5]

ArrayTwo

ClassPojo [Name = "XXX", FilterID = 4]

but when try to use:

 Arrays.asList(ArrayOne).contains(ArrayTwo )

or

ArrayOne().containsAll(ArrayTwo)

it returns false, i know the comparing is based on Refrences not Values equlaty but how i can do it by values note that: i want to use conatinsAll , so if the content of arrayTwo is found in some part of ArrayOne return true .

you are using very different method signatures. contains: https://docs.oracle.com/javase/8/docs/api/java/util/List.html#contains-java.lang.Object- Is for a ClassPojo element, not the List. containsAll -https://docs.oracle.com/javase/8/docs/api/java/util/List.html#containsAll-java.util.Collection - does take a list, but as mentioned in lots of comments below you need to implement equals method. — Bojan Petkovic, Apr 10 '17 at 18:57

score 7 · Answer 1 · edited Apr 10 '17 at 19:08

7

i know the comparing is based on references not Values equality

No, it is based on value equality. You need to override equals() to properly compare 2 objects of your ClassPojo

edited Apr 10 '17 at 19:08

RamPrakash

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answered Apr 10 '17 at 18:52

jmj

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so why it return false then? – Hesham El-Nemr Apr 10 '17 at 19:59
It uses `equals()` of `Object` inherited. which says `false` – jmj Apr 10 '17 at 20:00
so why it return false , there is two same values with filterID=4 – Hesham El-Nemr Apr 10 '17 at 20:08
debug in your IDE. put a breakpoint in `java.lang.Object#equals()` – jmj Apr 10 '17 at 20:11
i'm don't use equals() , i'm using ArrayOne().containsAll(ArrayTwo) , and i have tested it and it returns false – Hesham El-Nemr Apr 10 '17 at 20:21
it gets called internally. – jmj Apr 10 '17 at 21:44

Niki van Stein · Accepted Answer · 2017-04-11T05:50:41.613

3

In order for the contains or containsall to work you need to override the equals() function in your class ClassPojo.

It could look like this :

@Override
public boolean equals(Object obj){
    if (obj.Name.equals(this.Name) && obj.FilterID == this.FilterID)
        return true;
    else
        return false;
}

(written using phone so be careful with just copy paste)

edited Apr 11 '17 at 05:50

answered Apr 10 '17 at 18:54

Niki van Stein

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method does not override method from its superclass – Hesham El-Nemr Apr 10 '17 at 19:04
cannot reslove method equals (equals(this.FilterID)) for int – Hesham El-Nemr Apr 10 '17 at 19:24
Check, indeed, updated code. – Niki van Stein Apr 11 '17 at 05:51

containsAll return False when comparing two ArrayList of object

2 Answers2